High quality fuels remain in high demand. Fischer-Tropsch synthesis, which involves the production of hydrocarbons by the catalyzed reaction of mixtures of carbon monoxide (CO) and hydrogen (H2), also referred to as synthesis gas or syngas, can convert natural gas derived synthesis gas to liquid fuels and high-value chemicals. Fischer-Tropsch synthesis is one of the more attractive, direct and environmentally acceptable paths to high quality transportation fuels derived from natural gas.
Fischer-Tropsch catalysts are typically based on group VIII metals such as, for example, iron, cobalt, nickel and ruthenium. Such known catalysts are nonselective for a particularly desired product distribution, namely high levels of C5+ products and low levels of light gas. Processes using such catalyst are generally governed by the Anderson-Schulz-Flory (ASF) polymerization kinetics.
Hybrid Fischer-Tropsch catalysts including a Fischer-Tropsch component and an acidic component, such as a zeolite, have been found to be capable of limiting product chain growth in the Fischer-Tropsch reaction to a desired product distribution. Ruthenium, usually known as a promoter for cobalt, is a Fischer-Tropsch active metal that provides surprisingly low methane formation when used as the primary Fischer-Tropsch component Impregnation of a zeolite using an aqueous ruthenium solution followed by calcination, and activation by a reduction-oxidation-reduction cycle, as disclosed in copending U.S. patent application Ser. No. 12/797,439, reduces ruthenium ion-exchange with zeolite acid sites, thereby increasing the overall activity of the zeolite component. However, a certain fraction of ruthenium migrates into the zeolite pores and, after reduction, exists as reduced nanoclusters in the zeolite channels. Because ruthenium-catalyzed Fischer-Tropsch products are of much higher molecular weight than those from analogous cobalt-catalyzed reactions, the heavy wax is slow to diffuse out of the zeolite pores and effectively depresses the overall catalytic activity.
What is needed is a hybrid Fischer-Tropsch catalyst containing ruthenium, with its propensity for low light gas production, which limits product chain growth in the Fischer-Tropsch reaction and avoids the difficulties caused by ruthenium migrating into the pores of the support, and a method for forming such a Fischer-Tropsch catalyst. It would further be desirable to form a hydrocarbon product having a C21+ paraffin content of 5% or less.